1. Field of the Invention
The present invention generally relates to a permanent magnet rotating electric machine.
2. Description of the Related Art
The first reference, i.e. Japanese Unexamined Patent Application Publication No. 10-126981 describes conventional techniques of straight-shaping each of teeth of a stator of a permanent magnet rotating electric machine so as to reduce cogging torque of the permanent magnet rotating electric machine. Further, The second reference, i.e. Japanese Unexamined Patent Application Publication No. 11-089197 describes techniques of enhancing a demagnetization resistance by forming teeth of a stator and permanent magnets of a rotor into predetermined shapes.
Generally, in a permanent magnet rotating electric machine, pulsation of magnetic flux occurs because of the fact that a magnetic flux density does not change in a sinusoidal manner owing to the structure of the rotating electric machine. Thus, according to the techniques described in the first reference, cogging torque is reduced by straight-shaping the teeth of the stator. However, in the case of using such a rotating electric machine as a generator, a distortion factor of the waveform of an induced voltage rather than cogging torque turns into a problem. Incidentally, the distortion factor R (%) of the waveform of an induced voltage is defined by the following equation (1) obtained by Fourier series expansion of the waveform of the induced voltage:                     R        =                                                            ∑                                  i                  =                  2                                N                            ⁢                              xe2x80x83                            ⁢                              f                ⁡                                  (                  i                  )                                                                    F              ⁡                              (                l                )                                              xc3x97          100                                    (        1        )            
where f(N)is an effective value of Nth degree frequency component.
However, the first reference does not refer to the distortion factor of the waveform of an induced voltage.
Further, the invention disclosed in the second reference is directed to the improvement of a unique magnetic path for enhancing demagnetization resistance. However, the second reference does not refer to the distortion factor of the waveform of an induced voltage.
Accordingly, in view of the aforementioned problems, an object of the present invention is to provide a permanent magnet rotating electric machine wherein the distortion factor of the waveform of an induced voltage is reduced.
To achieve the foregoing object, according to an aspect of the present invention, there is provided a permanent magnet rotating electric machine comprising a stator having concentrated windings wound around teeth formed in a stator core, and a rotor having rare earth permanent magnets inserted into a plurality of permanent magnet holes formed in a rotor core. In this rotating electric machine, the permanent magnets are each shaped like an arc facing toward the stator. Moreover, a flat surface facing toward the rotor is provided at a tip end portion of each of teeth of the stator.
Incidentally, the width Wm (deg.) of the permanent magnet is given by
Wm=C1xc2x7Pr
where C1 is a magnet width coefficient and Pr (deg.) is a rotor pole pitch. In this case, preferably, the magnet width coefficient is set so that 0.75xe2x89xa6C1xe2x89xa60.85. Incidentally, the width Wm of the permanent magnet is defined herein as an angle between two straight lines passing through the center of a rotating shaft and respective ends of the magnet. Further, the width Wt (deg.) of a tip end portion of each of the teeth of the stator is expressed by
Wt=C2xc2x7Ps
where C2 is a stator width coefficient and Ps (deg.) is a stator slot pitch. In this case, preferably, the stator width coefficient is set so that 0.75xe2x89xa6C2xe2x89xa60.85. Incidentally, the width Wt of the tip end portion of each of the teeth of the stator is defined herein as an angle between two straight lines passing through the center of a rotating shaft and respective ends of the tip end portion of each of the teeth of the stator.